First of all the standard series, the safest (and most effective) way to be protected from tetanus, has nothing to do with horses. Secondly, if you have the standard series, and keep up the boosters about every 10 years, you would never need antiserum. Finally, they no longer use horse antiserum and have not for many years. Now they use human antisera. Antiserum is very expensive and dangerous even if you are not hypersensitive to it. It is only used to save your life if you have not done the smart thing and become immunized long ago. That is why you need to get the standard series and keep it up.

Of course, that series takes at least several months to give you any protection and that means you need to "fix the roof while the sun is shining". PREVENTION, PREVENTION, PREVENTION! The antiserum works the same day but only lasts a few months.